Owners must pay a one-time fee of $2,500 to activate the self-driving software on newer models with the required Autopilot hardware, which includes a forward-looking camera, radar and ultrasonic sensors.

Autopilot is not available for a retrofit on older models. Approximately 60,000 Model S sedans built since last fall now have autonomous capability.

"We're being especially cautious at this early stage," said Tesla CEO Elon Musk in a Wednesday media conference call. "We're advising keep your hands on the wheel."

He added: "In the long term, people will not need to have their hands on the wheel — and, eventually, there won't be wheels and pedals."

Although Autopilot is not fully self-driving, it enables Tesla vehicles to automatically steer, change lanes and adjust speed in response to traffic. The software update also features a new look for the Model S digital displays.

"Tesla Autopilot relieves drivers of the most tedious and potentially dangerous aspects of road travel," Tesla said in a statement. "While truly driverless cars are still a few years away, Tesla Autopilot functions like the systems that airplane pilots use when conditions are clear. The driver is still responsible for, and ultimately in control of, the car."

"We essentially try to make the car behave as if it's a really good chauffeur," Musk said.

But he emphasized that if the car is involved in a collision, the driver is still responsible.

"We're not yet at the point where the driver can abdicate responsibility," Musk said.

While a fully autonomous Tesla vehicle is still several years away, Musk said the current Autopilot is expected to be "quite a profound experience for people."

"At Tesla, we try to pioneer new technology," Musk said. "The two most profound innovations in automotive since the moving production line are electrification and autonomy. Those make a difference."

Edmunds says: After having been teased with Tesla's Autopilot feature for some time, Model S owners can finally give it a try, provided they have a newer model with the right equipment.